Uzi - Design

Design

The Uzi uses an open bolt, blowback-operated design quite similar to the Jaroslav Holeček-designed Czech ZK 476 (prototype only) and the production Sa 23, Sa 24, Sa 25, and Sa 26 series of submachineguns, from which it was inspired. The open bolt design exposes the breech end of the barrel, and improves cooling during periods of continuous fire. However, it means that since the bolt is held to the rear when cocked, the receiver is more susceptible to contamination from sand and dirt ingress. It uses a telescoping bolt design, in which the bolt wraps around the breech end of the barrel. This allows the barrel to be moved far back into the receiver and the magazine to be housed in the pistol grip, allowing for a heavier, slower-firing bolt in a shorter, better-balanced weapon.

The weapon is constructed primarily from stamped sheet metal, making it less expensive per unit to manufacture than an equivalent design machined from forgings. With relatively few moving parts, the Uzi is easy to strip for maintenance or repair. The magazine is housed within the pistol grip, allowing for intuitive and easy reloading in dark or difficult conditions, under the principle of "hand finds hand". The pistol grip is fitted with a grip safety, making it difficult to fire accidentally. However, the protruding vertical magazine makes the gun awkward to fire when prone. The Uzi features a bayonet lug.

Controls are relatively simple. The non reciprocating charging handle on the top of the receiver cover is used to retract the bolt. Submachine gun variants have a ratchet safety mechanism which will catch the bolt and lock its movement if it is retracted past the magazine, but not far enough to engage the sear. Semiauto civilian market versions of the Uzi usually do not have or need this feature. When the handle is fully retracted to the rear, the bolt will cock/catch on the sear mechanism and the handle can then be released to spring fully forward under power of a small spring attaching it to the topcover. It will remain forward during firing of the weapon since it does not reciprocate when the bolt is thrust backward by the force of a cartridge firing, or forward by the main action spring. The military/police versions of the Uzi will fire immediately upon chambering a cartridge as the Uzi is an open bolt weapon. This feature is extensively modified on commercial market semiauto Uzis in order to prevent fully automatic fire. The semiauto variants (whether rifle or pistol) fire from the closed bolt, with the entire bolt mechanism designed as a two-piece mechanism. The main bolt functions much like the original, but will close upon release of the charging handle. A mechanism containing part of the shape of the bolt and firing pin remains cocked to the rear. That striker like mechanism is only released forward when the trigger is pulled.

There are two external safety mechanisms on the Uzi, one being a selector lever which includes positions for "safe" which locks the sear and prevents movement of the bolt, "semi", which is one notch forward, which will allow the weapon to function in semiautomatic single shot mode, requiring the trigger to be pulled for each shot, and then "automatic" with the selector all the way forward, which will disengage part of the sear mechanism, allowing use of the trigger to control the firing mechanism. Once on automatic, the user may hold the trigger back and the weapon will fire until the magazine is empty. The bolt will then most likely come to rest on an empty chamber once the magazines is empty since the Uzi does not employ a bolt hold open on empty magazine mechanism like those found on military weapons that fire from the closed bolt. A very rare semiautomatic version made by FN Herstal and sold in Europe for a short time during the 1970s functioned exactly the same way, but the most forward setting on the selector lever was eliminated and blocked off. That variant was not approved for commercial import into the USA and was eventually withdrawn from production after having a relatively short commercial life in Western Europe and Canada.

The second external safety mechanism is a grip safety, located at the rear of the grip and meant to help prevent accidental discharge if the weapon is dropped, or the user loses a firm grip on the weapon during firing. The grip safety on the Uzi uses a stronger spring than that found on most handguns with a somewhat similar mechanism (US M1911, German Luger). The pistol grip must be firmly held by the user in order to allow the weapon to function, regardless of any manipulation of other controls.

The trigger mechanism is a conventional firearm trigger, but functions only to control the release mechanism for either the bolt (submachine gun) or firing pin holding mechanism (semiauto) since the UZI does not incorporate any internal cocking or hammer mechanism. While the system is much more mechanically simple than say, the Heckler & Koch MP5, it creates a noticeable delay from the point the user pulls the trigger and the point that the weapon actually fires. This delay is common with weapons that fire from the "open bolt".

The magazine release button/lever is located on the lower portion of the pistol grip and is intended to be manipulated by the non-firing hand. The paddle-like button lays flush with the pistol grip in order to help prevent accidental release of the magazine during soldier maneuvers and day to day activity.

Of the two stocks employed by the IDF, the wooden stock was the simpler and more robust of the two. The wooden stock is quick-detachable through the use of a release mechanism on the bottom side. Some commercial variants of the Uzi lacked the quick release mechanism and have the stock bolted in place. The second, and by far most popular stock on the Uzi was a unique folding stock which folds under the gun. It is robust but complex and was replaced by a side folding stock on the more compact models. Neither of the folding stocks can be quickly or easily removed from the weapon.

When the gun is de-cocked (the magazine must be removed or at least lowered enough to prevent feeding a round in the chamber in order to prevent the weapon from firing when it is being de-cocked), the ejector port closes, preventing entry of dust and dirt. Though the Uzi's stamped-metal receiver is equipped with pressed reinforcement slots to accept accumulated dirt and sand, the weapon can still jam with heavy accumulations of sand in desert combat conditions when not cleaned regularly. The magazine must be removed prior to "decocking" the weapon or else the bolt will feed a round when being let forward and then leave the firing pin resting on an unfired primer, which can then fire if the weapon is knocked or dropped. The decocking procedure is to remove the magazine, check the chamber (which should be empty) and then pull the trigger which will release the bolt to fall on the empty chamber. The magazine may then be re-inserted. To ready the weapon for firing again, the bolt handle must be retracted to the rear. Use of the selector switch is irrelevant to this process, except that it will prevent the bolt from moving when it is in the "safe" position.